[v8,01/17] Xen: ACPI: Hide UART used by Xen

Commit Message

Shannon Zhao March 25, 2016, 8:05 a.m. UTC

From: Shannon Zhao <[e-mail]>

ACPI 6.0 introduces a new table STAO to list the devices which are used
by Xen and can't be used by Dom0. On Xen virtual platforms, the physical
UART is used by Xen. So here it hides UART from Dom0.

CC: "Rafael J. Wysocki" <[e-mail]> (supporter:ACPI)
CC: Len Brown <[e-mail]> (supporter:ACPI)
CC: [e-mail] (open list:ACPI)
Signed-off-by: Shannon Zhao <[e-mail]>
---
 drivers/acpi/scan.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 68 insertions(+)

Comments

Rafael J. Wysocki March 25, 2016, 5 p.m. UTC | #1

On Friday, March 25, 2016 04:05:49 PM Shannon Zhao wrote:
> From: Shannon Zhao <[e-mail]>
> 
> ACPI 6.0 introduces a new table STAO to list the devices which are used
> by Xen and can't be used by Dom0. On Xen virtual platforms, the physical
> UART is used by Xen. So here it hides UART from Dom0.
> 
> CC: "Rafael J. Wysocki" <[e-mail]> (supporter:ACPI)
> CC: Len Brown <[e-mail]> (supporter:ACPI)
> CC: [e-mail] (open list:ACPI)
> Signed-off-by: Shannon Zhao <[e-mail]>

So I said it looked good, but now that I think about it, I have a question. ->

> ---
>  drivers/acpi/scan.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 68 insertions(+)
> 
> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> index 5f28cf7..5420cc5 100644
> --- a/drivers/acpi/scan.c
> +++ b/drivers/acpi/scan.c
> @@ -45,6 +45,7 @@ static LIST_HEAD(acpi_scan_handlers_list);
>  DEFINE_MUTEX(acpi_device_lock);
>  LIST_HEAD(acpi_wakeup_device_list);
>  static DEFINE_MUTEX(acpi_hp_context_lock);
> +static u64 spcr_uart_addr;
>  
>  struct acpi_dep_data {
>  	struct list_head node;
> @@ -1453,6 +1454,41 @@ static int acpi_add_single_object(struct acpi_device **child,
>  	return 0;
>  }
>  
> +static acpi_status acpi_get_resource_memory(struct acpi_resource *ares,
> +					    void *context)
> +{
> +	struct resource *res = context;
> +
> +	if (acpi_dev_resource_memory(ares, res))
> +		return AE_CTRL_TERMINATE;

-> It looks like this will terminate on the first memory resource found,
but what if there are more of them?

Or is it guaranteed that there will be only one for the device objects in
question?

If not, then it would better to check res.start == spcr_uart_addr here too
and only terminate if there's a match.

> +
> +	return AE_OK;
> +}
> +
> +static bool acpi_device_should_be_hidden(acpi_handle handle)
> +{
> +	acpi_status status;
> +	struct resource res;
> +
> +	/* Check if it should ignore the UART device */
> +	if (spcr_uart_addr != 0) {
> +		if (!acpi_has_method(handle, METHOD_NAME__CRS))
> +			return false;
> +
> +		status = acpi_walk_resources(handle, METHOD_NAME__CRS,
> +					     acpi_get_resource_memory, &res);
> +		if (ACPI_FAILURE(status))
> +			return false;
> +
> +		if (res.start == spcr_uart_addr) {
> +			printk(KERN_INFO PREFIX "The UART device in SPCR table will be hidden\n");
> +			return true;
> +		}
> +	}
> +
> +	return false;
> +}
> +
>  static int acpi_bus_type_and_status(acpi_handle handle, int *type,
>  				    unsigned long long *sta)
>  {
> @@ -1466,6 +1502,9 @@ static int acpi_bus_type_and_status(acpi_handle handle, int *type,
>  	switch (acpi_type) {
>  	case ACPI_TYPE_ANY:		/* for ACPI_ROOT_OBJECT */
>  	case ACPI_TYPE_DEVICE:
> +		if (acpi_device_should_be_hidden(handle))
> +			return -ENODEV;
> +
>  		*type = ACPI_BUS_TYPE_DEVICE;
>  		status = acpi_bus_get_status_handle(handle, sta);
>  		if (ACPI_FAILURE(status))
> @@ -1916,9 +1955,24 @@ static int acpi_bus_scan_fixed(void)
>  	return result < 0 ? result : 0;
>  }
>  
> +static void __init acpi_get_spcr_uart_addr(void)
> +{
> +	acpi_status status;
> +	struct acpi_table_spcr *spcr_ptr;
> +
> +	status = acpi_get_table(ACPI_SIG_SPCR, 0,
> +				(struct acpi_table_header **)&spcr_ptr);
> +	if (ACPI_SUCCESS(status))
> +		spcr_uart_addr = spcr_ptr->serial_port.address;
> +	else
> +		printk(KERN_WARNING PREFIX "STAO table present, but SPCR is missing\n");
> +}
> +
>  int __init acpi_scan_init(void)
>  {
>  	int result;
> +	acpi_status status;
> +	struct acpi_table_stao *stao_ptr;
>  
>  	acpi_pci_root_init();
>  	acpi_pci_link_init();
> @@ -1934,6 +1988,20 @@ int __init acpi_scan_init(void)
>  
>  	acpi_scan_add_handler(&generic_device_handler);
>  
> +	/*
> +	 * If there is STAO table, check whether it needs to ignore the UART
> +	 * device in SPCR table.
> +	 */
> +	status = acpi_get_table(ACPI_SIG_STAO, 0,
> +				(struct acpi_table_header **)&stao_ptr);
> +	if (ACPI_SUCCESS(status)) {
> +		if (stao_ptr->header.length > sizeof(struct acpi_table_stao))
> +			printk(KERN_INFO PREFIX "STAO Name List not yet supported.");
> +
> +		if (stao_ptr->ignore_uart)
> +			acpi_get_spcr_uart_addr();
> +	}
> +
>  	mutex_lock(&acpi_scan_lock);
>  	/*
>  	 * Enumerate devices in the ACPI namespace.
> 

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Bjorn Helgaas March 25, 2016, 5:15 p.m. UTC | #2

On Fri, Mar 25, 2016 at 04:05:49PM +0800, Shannon Zhao wrote:
> From: Shannon Zhao <[e-mail]>
> 
> ACPI 6.0 introduces a new table STAO to list the devices which are used
> by Xen and can't be used by Dom0. On Xen virtual platforms, the physical
> UART is used by Xen. So here it hides UART from Dom0.
> 
> CC: "Rafael J. Wysocki" <[e-mail]> (supporter:ACPI)
> CC: Len Brown <[e-mail]> (supporter:ACPI)
> CC: [e-mail] (open list:ACPI)
> Signed-off-by: Shannon Zhao <[e-mail]>
> ---
>  drivers/acpi/scan.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>  1 file changed, 68 insertions(+)
> 
> diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> index 5f28cf7..5420cc5 100644
> --- a/drivers/acpi/scan.c
> +++ b/drivers/acpi/scan.c
> @@ -45,6 +45,7 @@ static LIST_HEAD(acpi_scan_handlers_list);
>  DEFINE_MUTEX(acpi_device_lock);
>  LIST_HEAD(acpi_wakeup_device_list);
>  static DEFINE_MUTEX(acpi_hp_context_lock);
> +static u64 spcr_uart_addr;
>  
>  struct acpi_dep_data {
>  	struct list_head node;
> @@ -1453,6 +1454,41 @@ static int acpi_add_single_object(struct acpi_device **child,
>  	return 0;
>  }
>  
> +static acpi_status acpi_get_resource_memory(struct acpi_resource *ares,
> +					    void *context)
> +{
> +	struct resource *res = context;
> +
> +	if (acpi_dev_resource_memory(ares, res))
> +		return AE_CTRL_TERMINATE;
> +
> +	return AE_OK;
> +}
> +
> +static bool acpi_device_should_be_hidden(acpi_handle handle)
> +{
> +	acpi_status status;
> +	struct resource res;
> +
> +	/* Check if it should ignore the UART device */
> +	if (spcr_uart_addr != 0) {
> +		if (!acpi_has_method(handle, METHOD_NAME__CRS))
> +			return false;
> +
> +		status = acpi_walk_resources(handle, METHOD_NAME__CRS,
> +					     acpi_get_resource_memory, &res);
> +		if (ACPI_FAILURE(status))
> +			return false;
> +
> +		if (res.start == spcr_uart_addr) {
> +			printk(KERN_INFO PREFIX "The UART device in SPCR table will be hidden\n");

Can we at least print out the ACPI device path and address here for
debugging purposes?  IMHO, kernel messages that contain only static
text are always dubious.  There's almost always a useful address, IRQ,
return value, etc., that could be included.

> +			return true;
> +		}
> +	}
> +
> +	return false;
> +}
> +
>  static int acpi_bus_type_and_status(acpi_handle handle, int *type,
>  				    unsigned long long *sta)
>  {
> @@ -1466,6 +1502,9 @@ static int acpi_bus_type_and_status(acpi_handle handle, int *type,
>  	switch (acpi_type) {
>  	case ACPI_TYPE_ANY:		/* for ACPI_ROOT_OBJECT */
>  	case ACPI_TYPE_DEVICE:
> +		if (acpi_device_should_be_hidden(handle))
> +			return -ENODEV;
> +
>  		*type = ACPI_BUS_TYPE_DEVICE;
>  		status = acpi_bus_get_status_handle(handle, sta);
>  		if (ACPI_FAILURE(status))
> @@ -1916,9 +1955,24 @@ static int acpi_bus_scan_fixed(void)
>  	return result < 0 ? result : 0;
>  }
>  
> +static void __init acpi_get_spcr_uart_addr(void)
> +{
> +	acpi_status status;
> +	struct acpi_table_spcr *spcr_ptr;
> +
> +	status = acpi_get_table(ACPI_SIG_SPCR, 0,
> +				(struct acpi_table_header **)&spcr_ptr);
> +	if (ACPI_SUCCESS(status))
> +		spcr_uart_addr = spcr_ptr->serial_port.address;
> +	else
> +		printk(KERN_WARNING PREFIX "STAO table present, but SPCR is missing\n");
> +}
> +
>  int __init acpi_scan_init(void)
>  {
>  	int result;
> +	acpi_status status;
> +	struct acpi_table_stao *stao_ptr;
>  
>  	acpi_pci_root_init();
>  	acpi_pci_link_init();
> @@ -1934,6 +1988,20 @@ int __init acpi_scan_init(void)
>  
>  	acpi_scan_add_handler(&generic_device_handler);
>  
> +	/*
> +	 * If there is STAO table, check whether it needs to ignore the UART
> +	 * device in SPCR table.
> +	 */
> +	status = acpi_get_table(ACPI_SIG_STAO, 0,
> +				(struct acpi_table_header **)&stao_ptr);
> +	if (ACPI_SUCCESS(status)) {
> +		if (stao_ptr->header.length > sizeof(struct acpi_table_stao))
> +			printk(KERN_INFO PREFIX "STAO Name List not yet supported.");
> +
> +		if (stao_ptr->ignore_uart)
> +			acpi_get_spcr_uart_addr();
> +	}

This all seems sort of ad hoc.  Are UARTs the only things that can be
listed in STAO?  If STAO can contain things other than UARTs, are we
going to see more patches adding special-case code like this?

>  	mutex_lock(&acpi_scan_lock);
>  	/*
>  	 * Enumerate devices in the ACPI namespace.
> -- 
> 2.0.4
> 
> 
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Stefano Stabellini March 26, 2016, 12:44 p.m. UTC | #3

On Fri, 25 Mar 2016, Bjorn Helgaas wrote:
> On Fri, Mar 25, 2016 at 04:05:49PM +0800, Shannon Zhao wrote:
> > From: Shannon Zhao <[e-mail]>
> > 
> > ACPI 6.0 introduces a new table STAO to list the devices which are used
> > by Xen and can't be used by Dom0. On Xen virtual platforms, the physical
> > UART is used by Xen. So here it hides UART from Dom0.
> > 
> > CC: "Rafael J. Wysocki" <[e-mail]> (supporter:ACPI)
> > CC: Len Brown <[e-mail]> (supporter:ACPI)
> > CC: [e-mail] (open list:ACPI)
> > Signed-off-by: Shannon Zhao <[e-mail]>
> > ---
> >  drivers/acpi/scan.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 68 insertions(+)
> > 
> > diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> > index 5f28cf7..5420cc5 100644
> > --- a/drivers/acpi/scan.c
> > +++ b/drivers/acpi/scan.c
> > @@ -45,6 +45,7 @@ static LIST_HEAD(acpi_scan_handlers_list);
> >  DEFINE_MUTEX(acpi_device_lock);
> >  LIST_HEAD(acpi_wakeup_device_list);
> >  static DEFINE_MUTEX(acpi_hp_context_lock);
> > +static u64 spcr_uart_addr;
> >  
> >  struct acpi_dep_data {
> >  	struct list_head node;
> > @@ -1453,6 +1454,41 @@ static int acpi_add_single_object(struct acpi_device **child,
> >  	return 0;
> >  }
> >  
> > +static acpi_status acpi_get_resource_memory(struct acpi_resource *ares,
> > +					    void *context)
> > +{
> > +	struct resource *res = context;
> > +
> > +	if (acpi_dev_resource_memory(ares, res))
> > +		return AE_CTRL_TERMINATE;
> > +
> > +	return AE_OK;
> > +}
> > +
> > +static bool acpi_device_should_be_hidden(acpi_handle handle)
> > +{
> > +	acpi_status status;
> > +	struct resource res;
> > +
> > +	/* Check if it should ignore the UART device */
> > +	if (spcr_uart_addr != 0) {
> > +		if (!acpi_has_method(handle, METHOD_NAME__CRS))
> > +			return false;
> > +
> > +		status = acpi_walk_resources(handle, METHOD_NAME__CRS,
> > +					     acpi_get_resource_memory, &res);
> > +		if (ACPI_FAILURE(status))
> > +			return false;
> > +
> > +		if (res.start == spcr_uart_addr) {
> > +			printk(KERN_INFO PREFIX "The UART device in SPCR table will be hidden\n");
> 
> Can we at least print out the ACPI device path and address here for
> debugging purposes?  IMHO, kernel messages that contain only static
> text are always dubious.  There's almost always a useful address, IRQ,
> return value, etc., that could be included.
>
> > +			return true;
> > +		}
> > +	}
> > +
> > +	return false;
> > +}
> > +
> >  static int acpi_bus_type_and_status(acpi_handle handle, int *type,
> >  				    unsigned long long *sta)
> >  {
> > @@ -1466,6 +1502,9 @@ static int acpi_bus_type_and_status(acpi_handle handle, int *type,
> >  	switch (acpi_type) {
> >  	case ACPI_TYPE_ANY:		/* for ACPI_ROOT_OBJECT */
> >  	case ACPI_TYPE_DEVICE:
> > +		if (acpi_device_should_be_hidden(handle))
> > +			return -ENODEV;
> > +
> >  		*type = ACPI_BUS_TYPE_DEVICE;
> >  		status = acpi_bus_get_status_handle(handle, sta);
> >  		if (ACPI_FAILURE(status))
> > @@ -1916,9 +1955,24 @@ static int acpi_bus_scan_fixed(void)
> >  	return result < 0 ? result : 0;
> >  }
> >  
> > +static void __init acpi_get_spcr_uart_addr(void)
> > +{
> > +	acpi_status status;
> > +	struct acpi_table_spcr *spcr_ptr;
> > +
> > +	status = acpi_get_table(ACPI_SIG_SPCR, 0,
> > +				(struct acpi_table_header **)&spcr_ptr);
> > +	if (ACPI_SUCCESS(status))
> > +		spcr_uart_addr = spcr_ptr->serial_port.address;
> > +	else
> > +		printk(KERN_WARNING PREFIX "STAO table present, but SPCR is missing\n");
> > +}
> > +
> >  int __init acpi_scan_init(void)
> >  {
> >  	int result;
> > +	acpi_status status;
> > +	struct acpi_table_stao *stao_ptr;
> >  
> >  	acpi_pci_root_init();
> >  	acpi_pci_link_init();
> > @@ -1934,6 +1988,20 @@ int __init acpi_scan_init(void)
> >  
> >  	acpi_scan_add_handler(&generic_device_handler);
> >  
> > +	/*
> > +	 * If there is STAO table, check whether it needs to ignore the UART
> > +	 * device in SPCR table.
> > +	 */
> > +	status = acpi_get_table(ACPI_SIG_STAO, 0,
> > +				(struct acpi_table_header **)&stao_ptr);
> > +	if (ACPI_SUCCESS(status)) {
> > +		if (stao_ptr->header.length > sizeof(struct acpi_table_stao))
> > +			printk(KERN_INFO PREFIX "STAO Name List not yet supported.");
> > +
> > +		if (stao_ptr->ignore_uart)
> > +			acpi_get_spcr_uart_addr();
> > +	}
> 
> This all seems sort of ad hoc.  Are UARTs the only things that can be
> listed in STAO?  If STAO can contain things other than UARTs, are we
> going to see more patches adding special-case code like this?

The UART (specifically the UART described by the SPCR table) is the only
object which needs special-casing. Everything else is covered by ACPI
namespace paths (which is what the message above is about, given that it
is not supported by this patch).
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Stefano Stabellini March 26, 2016, 1:14 p.m. UTC | #4

On Fri, 25 Mar 2016, Rafael J. Wysocki wrote:
> On Friday, March 25, 2016 04:05:49 PM Shannon Zhao wrote:
> > From: Shannon Zhao <[e-mail]>
> > 
> > ACPI 6.0 introduces a new table STAO to list the devices which are used
> > by Xen and can't be used by Dom0. On Xen virtual platforms, the physical
> > UART is used by Xen. So here it hides UART from Dom0.
> > 
> > CC: "Rafael J. Wysocki" <[e-mail]> (supporter:ACPI)
> > CC: Len Brown <[e-mail]> (supporter:ACPI)
> > CC: [e-mail] (open list:ACPI)
> > Signed-off-by: Shannon Zhao <[e-mail]>
> 
> So I said it looked good, but now that I think about it, I have a question. ->
> 
> > ---
> >  drivers/acpi/scan.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++++
> >  1 file changed, 68 insertions(+)
> > 
> > diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
> > index 5f28cf7..5420cc5 100644
> > --- a/drivers/acpi/scan.c
> > +++ b/drivers/acpi/scan.c
> > @@ -45,6 +45,7 @@ static LIST_HEAD(acpi_scan_handlers_list);
> >  DEFINE_MUTEX(acpi_device_lock);
> >  LIST_HEAD(acpi_wakeup_device_list);
> >  static DEFINE_MUTEX(acpi_hp_context_lock);
> > +static u64 spcr_uart_addr;
> >  
> >  struct acpi_dep_data {
> >  	struct list_head node;
> > @@ -1453,6 +1454,41 @@ static int acpi_add_single_object(struct acpi_device **child,
> >  	return 0;
> >  }
> >  
> > +static acpi_status acpi_get_resource_memory(struct acpi_resource *ares,
> > +					    void *context)
> > +{
> > +	struct resource *res = context;
> > +
> > +	if (acpi_dev_resource_memory(ares, res))
> > +		return AE_CTRL_TERMINATE;
> 
> -> It looks like this will terminate on the first memory resource found,
> but what if there are more of them?
> 
> Or is it guaranteed that there will be only one for the device objects in
> question?

Given that spcr_uart_addr is actually the only Base Address specified by
the SPCR table, I think it is assumed that this kind of devices only
have one memory region.


> If not, then it would better to check res.start == spcr_uart_addr here too
> and only terminate if there's a match.
>
> > +
> > +	return AE_OK;
> > +}
> > +
> > +static bool acpi_device_should_be_hidden(acpi_handle handle)
> > +{
> > +	acpi_status status;
> > +	struct resource res;
> > +
> > +	/* Check if it should ignore the UART device */
> > +	if (spcr_uart_addr != 0) {
> > +		if (!acpi_has_method(handle, METHOD_NAME__CRS))
> > +			return false;
> > +
> > +		status = acpi_walk_resources(handle, METHOD_NAME__CRS,
> > +					     acpi_get_resource_memory, &res);
> > +		if (ACPI_FAILURE(status))
> > +			return false;
> > +
> > +		if (res.start == spcr_uart_addr) {
> > +			printk(KERN_INFO PREFIX "The UART device in SPCR table will be hidden\n");
> > +			return true;
> > +		}
> > +	}
> > +
> > +	return false;
> > +}
> > +
> >  static int acpi_bus_type_and_status(acpi_handle handle, int *type,
> >  				    unsigned long long *sta)
> >  {
> > @@ -1466,6 +1502,9 @@ static int acpi_bus_type_and_status(acpi_handle handle, int *type,
> >  	switch (acpi_type) {
> >  	case ACPI_TYPE_ANY:		/* for ACPI_ROOT_OBJECT */
> >  	case ACPI_TYPE_DEVICE:
> > +		if (acpi_device_should_be_hidden(handle))
> > +			return -ENODEV;
> > +
> >  		*type = ACPI_BUS_TYPE_DEVICE;
> >  		status = acpi_bus_get_status_handle(handle, sta);
> >  		if (ACPI_FAILURE(status))
> > @@ -1916,9 +1955,24 @@ static int acpi_bus_scan_fixed(void)
> >  	return result < 0 ? result : 0;
> >  }
> >  
> > +static void __init acpi_get_spcr_uart_addr(void)
> > +{
> > +	acpi_status status;
> > +	struct acpi_table_spcr *spcr_ptr;
> > +
> > +	status = acpi_get_table(ACPI_SIG_SPCR, 0,
> > +				(struct acpi_table_header **)&spcr_ptr);
> > +	if (ACPI_SUCCESS(status))
> > +		spcr_uart_addr = spcr_ptr->serial_port.address;
> > +	else
> > +		printk(KERN_WARNING PREFIX "STAO table present, but SPCR is missing\n");
> > +}
> > +
> >  int __init acpi_scan_init(void)
> >  {
> >  	int result;
> > +	acpi_status status;
> > +	struct acpi_table_stao *stao_ptr;
> >  
> >  	acpi_pci_root_init();
> >  	acpi_pci_link_init();
> > @@ -1934,6 +1988,20 @@ int __init acpi_scan_init(void)
> >  
> >  	acpi_scan_add_handler(&generic_device_handler);
> >  
> > +	/*
> > +	 * If there is STAO table, check whether it needs to ignore the UART
> > +	 * device in SPCR table.
> > +	 */
> > +	status = acpi_get_table(ACPI_SIG_STAO, 0,
> > +				(struct acpi_table_header **)&stao_ptr);
> > +	if (ACPI_SUCCESS(status)) {
> > +		if (stao_ptr->header.length > sizeof(struct acpi_table_stao))
> > +			printk(KERN_INFO PREFIX "STAO Name List not yet supported.");
> > +
> > +		if (stao_ptr->ignore_uart)
> > +			acpi_get_spcr_uart_addr();
> > +	}
> > +
> >  	mutex_lock(&acpi_scan_lock);
> >  	/*
> >  	 * Enumerate devices in the ACPI namespace.
> > 
> 
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Shannon Zhao March 29, 2016, 8 a.m. UTC | #5

On 2016/3/26 1:15, Bjorn Helgaas wrote:
> On Fri, Mar 25, 2016 at 04:05:49PM +0800, Shannon Zhao wrote:
>> > From: Shannon Zhao <[e-mail]>
>> > 
>> > ACPI 6.0 introduces a new table STAO to list the devices which are used
>> > by Xen and can't be used by Dom0. On Xen virtual platforms, the physical
>> > UART is used by Xen. So here it hides UART from Dom0.
>> > 
>> > CC: "Rafael J. Wysocki" <[e-mail]> (supporter:ACPI)
>> > CC: Len Brown <[e-mail]> (supporter:ACPI)
>> > CC: [e-mail] (open list:ACPI)
>> > Signed-off-by: Shannon Zhao <[e-mail]>
>> > ---
>> >  drivers/acpi/scan.c | 68 +++++++++++++++++++++++++++++++++++++++++++++++++++++
>> >  1 file changed, 68 insertions(+)
>> > 
>> > diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
>> > index 5f28cf7..5420cc5 100644
>> > --- a/drivers/acpi/scan.c
>> > +++ b/drivers/acpi/scan.c
>> > @@ -45,6 +45,7 @@ static LIST_HEAD(acpi_scan_handlers_list);
>> >  DEFINE_MUTEX(acpi_device_lock);
>> >  LIST_HEAD(acpi_wakeup_device_list);
>> >  static DEFINE_MUTEX(acpi_hp_context_lock);
>> > +static u64 spcr_uart_addr;
>> >  
>> >  struct acpi_dep_data {
>> >  	struct list_head node;
>> > @@ -1453,6 +1454,41 @@ static int acpi_add_single_object(struct acpi_device **child,
>> >  	return 0;
>> >  }
>> >  
>> > +static acpi_status acpi_get_resource_memory(struct acpi_resource *ares,
>> > +					    void *context)
>> > +{
>> > +	struct resource *res = context;
>> > +
>> > +	if (acpi_dev_resource_memory(ares, res))
>> > +		return AE_CTRL_TERMINATE;
>> > +
>> > +	return AE_OK;
>> > +}
>> > +
>> > +static bool acpi_device_should_be_hidden(acpi_handle handle)
>> > +{
>> > +	acpi_status status;
>> > +	struct resource res;
>> > +
>> > +	/* Check if it should ignore the UART device */
>> > +	if (spcr_uart_addr != 0) {
>> > +		if (!acpi_has_method(handle, METHOD_NAME__CRS))
>> > +			return false;
>> > +
>> > +		status = acpi_walk_resources(handle, METHOD_NAME__CRS,
>> > +					     acpi_get_resource_memory, &res);
>> > +		if (ACPI_FAILURE(status))
>> > +			return false;
>> > +
>> > +		if (res.start == spcr_uart_addr) {
>> > +			printk(KERN_INFO PREFIX "The UART device in SPCR table will be hidden\n");
> Can we at least print out the ACPI device path and address here for
> debugging purposes?  IMHO, kernel messages that contain only static
> text are always dubious.  There's almost always a useful address, IRQ,
> return value, etc., that could be included.
> 
Ok, I'll add the device address in the message and update this patch.

Thanks,

Patch

diff --git a/drivers/acpi/scan.c b/drivers/acpi/scan.c
index 5f28cf7..5420cc5 100644
--- a/drivers/acpi/scan.c
+++ b/drivers/acpi/scan.c
@@ -45,6 +45,7 @@  static LIST_HEAD(acpi_scan_handlers_list);
 DEFINE_MUTEX(acpi_device_lock);
 LIST_HEAD(acpi_wakeup_device_list);
 static DEFINE_MUTEX(acpi_hp_context_lock);
+static u64 spcr_uart_addr;
 
 struct acpi_dep_data {
 	struct list_head node;
@@ -1453,6 +1454,41 @@  static int acpi_add_single_object(struct acpi_device **child,
 	return 0;
 }
 
+static acpi_status acpi_get_resource_memory(struct acpi_resource *ares,
+					    void *context)
+{
+	struct resource *res = context;
+
+	if (acpi_dev_resource_memory(ares, res))
+		return AE_CTRL_TERMINATE;
+
+	return AE_OK;
+}
+
+static bool acpi_device_should_be_hidden(acpi_handle handle)
+{
+	acpi_status status;
+	struct resource res;
+
+	/* Check if it should ignore the UART device */
+	if (spcr_uart_addr != 0) {
+		if (!acpi_has_method(handle, METHOD_NAME__CRS))
+			return false;
+
+		status = acpi_walk_resources(handle, METHOD_NAME__CRS,
+					     acpi_get_resource_memory, &res);
+		if (ACPI_FAILURE(status))
+			return false;
+
+		if (res.start == spcr_uart_addr) {
+			printk(KERN_INFO PREFIX "The UART device in SPCR table will be hidden\n");
+			return true;
+		}
+	}
+
+	return false;
+}
+
 static int acpi_bus_type_and_status(acpi_handle handle, int *type,
 				    unsigned long long *sta)
 {
@@ -1466,6 +1502,9 @@  static int acpi_bus_type_and_status(acpi_handle handle, int *type,
 	switch (acpi_type) {
 	case ACPI_TYPE_ANY:		/* for ACPI_ROOT_OBJECT */
 	case ACPI_TYPE_DEVICE:
+		if (acpi_device_should_be_hidden(handle))
+			return -ENODEV;
+
 		*type = ACPI_BUS_TYPE_DEVICE;
 		status = acpi_bus_get_status_handle(handle, sta);
 		if (ACPI_FAILURE(status))
@@ -1916,9 +1955,24 @@  static int acpi_bus_scan_fixed(void)
 	return result < 0 ? result : 0;
 }
 
+static void __init acpi_get_spcr_uart_addr(void)
+{
+	acpi_status status;
+	struct acpi_table_spcr *spcr_ptr;
+
+	status = acpi_get_table(ACPI_SIG_SPCR, 0,
+				(struct acpi_table_header **)&spcr_ptr);
+	if (ACPI_SUCCESS(status))
+		spcr_uart_addr = spcr_ptr->serial_port.address;
+	else
+		printk(KERN_WARNING PREFIX "STAO table present, but SPCR is missing\n");
+}
+
 int __init acpi_scan_init(void)
 {
 	int result;
+	acpi_status status;
+	struct acpi_table_stao *stao_ptr;
 
 	acpi_pci_root_init();
 	acpi_pci_link_init();
@@ -1934,6 +1988,20 @@  int __init acpi_scan_init(void)
 
 	acpi_scan_add_handler(&generic_device_handler);
 
+	/*
+	 * If there is STAO table, check whether it needs to ignore the UART
+	 * device in SPCR table.
+	 */
+	status = acpi_get_table(ACPI_SIG_STAO, 0,
+				(struct acpi_table_header **)&stao_ptr);
+	if (ACPI_SUCCESS(status)) {
+		if (stao_ptr->header.length > sizeof(struct acpi_table_stao))
+			printk(KERN_INFO PREFIX "STAO Name List not yet supported.");
+
+		if (stao_ptr->ignore_uart)
+			acpi_get_spcr_uart_addr();
+	}
+
 	mutex_lock(&acpi_scan_lock);
 	/*
 	 * Enumerate devices in the ACPI namespace.